The present invention relates to a vacuum degassing apparatus for molten glass, which removes bubbles from molten glass continuously supplied, and a method for building the apparatus.
In order to improve the quality of formed glass products, there has been used a vacuum degassing apparatus which removes bubbles generated in a molten glass before the molten glass that has been molten in a melting tank is formed by a forming apparatus, as shown in FIG. 4.
The vacuum degassing apparatus 110 shown in FIG. 4 is used in a process wherein molten glass G in a melting vessel 120 is vacuum-degassed and is continuously supplied to a subsequent treatment vessel. In the vacuum degassing apparatus are provided a vacuum housing 112 which is evacuated to be depressurized therein for vacuum-degassing the molten glass, a vacuum degassing vessel 114 which is provided in the vacuum housing 112 and is depressurized together with the vacuum housing, and an uprising pipe 116 and a downfalling pipe 118 which are connected to respective end portions of the vacuum degassing vessel in a downward and vertical direction. The uprising pipe 116 has a lower end immersed in the molten glass G in an upstream pit 122 in communication with the melting vessel 120. Likewise, the downfalling pipe 118 has a lower end immersed in the molten glass G in a downstream pit 124 in communication with the subsequent treatment vessel (not shown).
The vacuum degassing vessel 114 is substantially horizontally provided in the vacuum housing 112 which is evacuated through a suction port 112c by a vacuum pump, not shown, to be depressurized therein. Since the inside of the vacuum degassing vessel 114 is depressurized, through suction ports 114a and 114b in communication with the inside of the vacuum housing 112, to a pressure of {fraction (1/20)}-⅓ atmosphere together with the inside of the vacuum housing 112, the molten glass G in the upstream pit 122 before degassing is sucked and drawn up by the uprising pipe 116, and is introduced into the vacuum degassing vessel 114. After the molten glass has been vacuum-degassed in the vacuum degassing vessel 114, the molten glass is drawn down by the downfalling pipe 118 to be discharged into the downstream pit 124.
The vacuum housing 112 may be a casing made of metal, such as stainless steel and heat-resisting steel. The vacuum housing is evacuated by the vacuum pump, not shown, for instance, to be depressurized therein, maintaining the inside of the vacuum degassing vessel 114 provided therein in a depressurized state, such as a pressure of {fraction (1/20)}⅓ atmosphere. In the vacuum degassing vessel 114 is formed an upper space 114s above the molten glass which has been filled at a certain depth in the vacuum degassing vessel.
Around the vacuum degassing vessel 114, the uprising pipe 116 and the downfalling pipe 118 in the vacuum housing 112 is provided thermal insulation material 130, such as refractory bricks, to cover these members for thermal insulation.
Since the conventional vacuum degassing apparatus 110 is configured to deal with the molten glass G having a high temperature, such as a temperature at 1,200-1,400xc2x0 C., paths for molten glass in direct contact with the molten glass G, such as the vacuum degassing vessel 114, the uprising pipe 116 and the downfalling pipe 118, are constituted by circular shells, which are made of noble metal, such as platinum and platinum alloy, as shown in JP-A-2221129 in the name of the applicants.
The reason why the paths for molten glass, such as the vacuum degassing vessel 114, the uprising pipe 116 and the downfalling pipe 118, are made of noble metal, such as platinum and platinum alloy, is that there is no inclusion of impurities into the molten glass G and a certain strength is ensured at high temperatures since it is hardly possible due to low reactivity of the noble metal with the molten glass at a high temperature that, when the noble metal contacts the molten glass G at such a high temperature, the noble metal elutes by reaction with the molten glass G.
When the vacuum degassing vessel 114 is constituted by a circular shell made of noble metal, an increase in the wall thickness of the shell directly and significantly rises the cost since noble metal such as platinum is quite expensive. From this viewpoint, the diameter of the circular shell is limited to a certain value in terms of cost and strength, and it is difficult to significantly increase the diameter of the circular shell. This creates a problem in that the quantity of the molten glass G to be vacuum-degassed in the vacuum degassing vessel 114 is limited to a certain level, and that it is impossible to build the vacuum degassing apparatus so as to have a large throughput.
Since the molten glass G is obtained by dissolution reaction of powders raw material, it is preferable that the temperature in the melting vessel 120 is high in dissolution. Since the viscosity of the molten glass G decreases at high temperatures, it is preferable that the temperature of the molten glass is high in vacuum-degassing. Although the conventional vacuum degassing apparatus requires to use alloy with noble metal included therein in the vacuum degassing vessel 114 and the like in terms of high temperature strength, it is difficult to increase the wall thickness of the circular shells in terms of cost because noble metal is expensive. Even if noble metal, such as platinum, is used, the strength thereof inevitably lowers as the temperature becomes higher. As a result, the temperature of the molten glass at an inlet of the vacuum degassing apparatus 110 has been limited to the certain temperature (1,200-1,400xc2x0 C.) as stated earlier.
When the paths for the molten glass having a high temperature are made of platinum, the formation of holes due to wearing of the thin platinum must be taken into account in designing, and the apparatus is required to be configured so as to enable to repair and replacement of platinum for a short period of time after the production of glass products has been temporarily standstill. Since the paths made of platinum (the vacuum degassing vessel, the uprising pipe and the downfalling pipe) in the conventional vacuum degassing apparatus are provided in series, repair and replacement of the paths has required to release the depressurized state and expel all the molten glass from the inside of the vacuum vessel, the uprising pipe and the downfalling pipe, to drop the temperature of the entire vacuum apparatus to an ordinary temperature, and then to carry out repair or replacement of platinum. Since it is appropriate that the molten glass is cut at the lower ends of the uprising and downfalling pipes for repair or replacement of platinum, the vacuum degassing apparatus has been required to have a structure that the entire apparatus can be lifted by at least 1 m to separate the uprising and downfalling pipes from the high temperature glass reservoirs thereunder when, in particular, the uprising pipe and the downfalling pipe are repaired. However, lifting the entire vacuum degassing apparatus 110 has required an extremely difficult operation since the apparatus is large and extremely heavy in consideration of the operation at a high temperature and in the depressurized state.
As stated earlier, it is difficult to provide the apparatus in a large size in terms of cost since platinum or platinum rhodium, which has low reactivity at high temperatures, is expensive. Even if the apparatus is build in a large size, it is impossible to provide the circular shells with a sufficient wall thickness. As a result, it is impossible to obtain strength required to resist heat. This prevents the temperature of the molten glass from being raised, making it difficult to decrease the viscosity of the molten glass so as to exhibit a vacuum-degassing effect in a sufficient way. Since the provision of an insufficient wall thickness needs repair or replacement required by wearing, accompanied by difficult operation, it is practically difficult to build the apparatus in a large size and to provide the apparatus with a large throughput.
In order to cope with this problem, a proposal is made to build the vacuum degassing apparatus in a large size and to increase the vacuum-degassing amount by using refractory brick to constitute the vacuum degassing vessel 114, the uprising pipe 116 and the downfalling pipe 118 in the conventional vacuum degassing apparatus 110 shown in FIG. 4. However, it is absolutely impossible to build each of the vacuum degassing vessel 114, the uprising pipe 116 and the downfalling pipe 118 by a single piece of refractory brick since there are limitations on preparation of refractory brick in a large size. In order to build each of the vacuum degassing vessel 114, the uprising pipe 116 and the downfalling pipe 118 in the vacuum degassing apparatus 110 by refractory brick, many pieces of refractory brick are required to be combined. This inevitably provides joints, in the paths in direct contact with the molten glass, which connect pieces of refractory brick.
When the vacuum degassing vessel 114, the uprising pipe 116 and the downfalling pipe 118 in the vacuum degassing apparatus 110 are made of refractory brick, the use of dense refractory brick, such as electro-cast refractory material, as the refractory brick in direct contact with the molten glass is considered since some components inevitably elute into the molten glass from the refractory brick in direct contact with the molten glass. Even if denser refractory brick is used as the refractory brick to be used in these members, there are created problems in that the molten glass leaks through a gap at a joint to dissolve and erode backup refractory brick or thermal insulation material behind the dense refractory brick, thereby causing the components thereof dissolved into the molten glass to degrade the quality of products, and that, even if the degree of erosion in the dense refractory brick is small, the backup refractory brick or the thermal insulation material is eroded by the molten glass to shorten the life of the vacuum degassing apparatus 110 in per se.
In order to cope with this problem, it is considered to fill jointing material in joints between pieces of refractory brick forming the paths in direct with the molten glass. However, there is created a problem in that the joint material in direct contact with the molten glass is easily eroded in comparison with refractory brick since the joint material is generally less dense in comparison with the refractory brick, in particular dense refractory brick, and that, even if the degree of erosion in the refractory brick in per se is small, the erosion in joints between pieces of refractory brick selectively develops. Although the life of the vacuum degassing apparatus is slightly lengthened in comparison with lack of joint material in the joints, the backup refractory brick or the thermal insulation material behind the dense refractory brick is dissolved and eroded as stated earlier after erosion of the joint material, creating problems in that the quality of products degrades and the life of the vacuum degassing apparatus 110 in per se becomes shorter.
It is an object of the present invention to solve these problems, and to provide a vacuum degassing apparatus for molten glass capable of being used in a long period of time by preventing or restraining molten glass from leaking through a joint between pieces of refractory brick in direct contact with the molten glass or by preventing backup refractory material or thermal insulation refractory material from being eroded even if the molten glass leaks through the joint, and to provide a method for building the apparatus as well. In order to decrease the building cost of the apparatus and improve the design freedom of the apparatus to provide the apparatus with a large throughput, the apparatus has a vacuum degassing vessel, an uprising pipe and a downfalling pipe constituted by combining inexpensive refractory bricks in comparison with noble metal such as platinum and noble alloy.
In order to attain the object, the present invention, as a first mode, provides a vacuum degassing apparatus for molten glass, comprising a vacuum housing which is evacuated to be depressurized therein; a vacuum degassing vessel which is provided in the vacuum housing to vacuum-degas molten glass; an uprising pipe which connects to the vacuum degassing vessel, and sucks and draws up undegassed molten glass to introduce the undegassed molten glass into the vacuum degassing vessel; and a downfalling pipe which connects to the vacuum degassing vessel and draws down the degassed molten glass from the vacuum degassing vessel to discharge the degassed molten glass; wherein paths in direct contact with the molten lo glass are made of assembled dense refractory bricks, the paths providing the vacuum degassing vessel, at least one portion of the uprising pipe and at lease one portion of the downfalling pipe, and the bricks have a flatness of not greater than 0.5 mm on contacting surfaces with adjoining dense refractory bricks.
It is preferable that an inner surface brick layer has a flatness of not greater than 0.25 mm on the contacting surfaces with adjoining dense refractory bricks.
It is preferable that the dense refractory material is at least one of at least one electro-cast refractory material among alumina based electro-cast refractory material, zirconia based electro-cast refractory material and alumina-zirconia-silica based electro-cast refractory material, and at least one dense burned refractory material among dense alumina based refractory material, dense zirconia-silica based refractory material and dense alumina-zirconia-silica based refractory material.
The present invention, as a second mode, provides a vacuum degassing apparatus for molten glass, comprising a vacuum housing which is evacuated to be depressurized therein; a vacuum degassing vessel which is provided in the vacuum housing to vacuum-degas molten glass; an uprising pipe which connects to the vacuum degassing vessel, and sucks and draws up undegassed molten glass to introduce the undegassed molten glass into the vacuum degassing vessel; and a downfalling pipe which connects to the vacuum degassing vessel and draws down the degassed molten glass from the vacuum degassing vessel to discharge the degassed molten glass; wherein each of the vacuum degassing vessel, at least one portion of the uprising pipe and at lease one portion of the downfalling pipe includes an inner surface brick layer made of assembled dense refractory bricks and forming a path in direct contact with the molten glass, at least one backup brick layer provided behind the inner brick layer and made of assembled refractory bricks, and a ramming material layer provided in at least a space between the inner surface layer and the backup brick layer adjoining thereto and filled with ramming material.
It is preferable that at least two backup brick layers are provided and that a ramming layer with the ramming material filled therein is provided at a space between the adjoining backup brick layers.
It is preferable that at least a space between the inner surface brick layer and the backup brick layer adjoining thereto has a size of 20-50 mm.
It is preferable that the inner surface brick layer and the at least one backup brick layer are made of the bricks assembled so that joints with adjoining bricks in one brick layer do not overlap with joints with adjoining bricks in the other brick layer by a length greater than that of the joints in the other brick layer.
It is preferable that the refractory bricks forming the backup brick layer are dense refractory bricks.
It is preferable that the ramming material is at least one or a mixture of two among alumina based ramming material, zirconia-silica based ramming material, and alumina-zirconia-silica based ramming material.
It is preferable that the ramming material has a water content of 3 to 15 wt % used for kneading thereof.
It is preferable that the bricks in the inner surface layer have a flatness of not greater than 0.5 mm, particularly 0.25 mm on contacting surfaces with adjoining dense refractory bricks.
It is preferable that the dense refractory brick is at least one of at least one electro-cast refractory material among alumina based electro-cast refractory material, zirconia based electro-cast refractory material and alumina-zirconia-silica based electro-cast refractory material, and at least one dense burned refractory material among dense alumina based refractory material, dense zirconia-silica based refractory material and dense alumina-zirconia-silica based refractory material.
The present invention, as a third mode, provides a method for building a vacuum degassing apparatus for molten glass, comprising a vacuum housing which is evacuated to be depressurized therein; a vacuum degassing vessel which is provided in the vacuum housing to vacuum-degas molten glass; an uprising pipe which connects to the vacuum degassing vessel, and sucks and draws up undegassed molten glass to introduce the undegassed molten glass into the vacuum degassing vessel; and a downfalling pipe which connects to the vacuum degassing vessel and draws down the degassed molten glass from the vacuum degassing vessel to discharge the degassed molten glass; wherein each of paths in series that comprise the vacuum degassing vessel, at least one portion of the uprising pipe and at lease one portion of the downfalling pipe is provided by polishing contacting surfaces of dense refractory bricks with adjoining dense refractory bricks to provide a flatness of not greater than 0.5 mm on the contacting surfaces, assembling the polished bricks to provide each of the paths in direct contact with the molten glass as the vacuum degassing vessel, the at least one portion of the uprising pipe and the at least one portion of the downfalling pipe, heating the paths to a certain temperature to elute vitreous substance from the dense refractory bricks, and filling spaces between the contacting surfaces of the adjoining bricks with the vitreous substance.
The present invention, as a fourth mode, provides a method for building a vacuum degassing apparatus for molten glass, comprising a vacuum housing which is evacuated to be depressurized therein; a vacuum degassing vessel which is provided in the vacuum housing to vacuum-degas molten glass; an uprising pipe which connects to the vacuum degassing vessel, and sucks and draws up undegassed molten glass to introduce the undegassed molten glass into the vacuum degassing vessel; and a downfalling pipe which connects to the vacuum degassing vessel and draws down the degassed molten glass from the vacuum degassing vessel to discharge the degassed molten glass; wherein among paths in series which comprise the vacuum degassing vessel, at least one portion of the uprising pipe and at lease one portion of the downfalling pipe, portions of the paths in direct contact with the molten glass are provided with an inner surface brick layer made of assembled dense refractory bricks, at least one backup brick layer made of assembled refractory bricks is provided behind the inner surface brick layer so as to be spaced from the inner surface brick layer by a certain distance, and ramming material with a small amount of water kneaded therewith is filled in at least a space between the inner surface brick layer and the backup brick layer, being subjected to vibration by a vibrator.
It is preferable that the inner surface brick layer is provided by polishing contacting surfaces of the dense refractory bricks with adjoining dense refractory bricks to provide a flatness of not greater than 0.5 mm on the contacting surfaces, assembling the polished bricks to provide each of the paths in direct contact with the molten glass as the vacuum degassing vessel, the at least one portion of the uprising pipe and the at least one portion of the downfalling pipe, heating the paths to a certain temperature to elute vitreous substance from the dense refractory bricks, and filling spaces between the contacting surfaces of the adjoining bricks with the vitreous substance.